...existing drivers pushed to unemployment
The problem is not only that, but the lack of job openings for new drivers (and similarly in all other industries being automated). In the worst case, there will be a horde of youngsters with no gainful employment. Not all can be robotics designers or in other high-skill jobs. This would be a volatile situation. Lots of unemployed young men is one major reason for the mess in the Middle-East, and in other troublespots.